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Thesis (Ph. D.)--Lehigh University, 2005. / Includes vita. Includes bibliographical references (leaves 146-152).

Thesis (Ph. D.)--Lehigh University, 2005. / Includes vita. Includes bibliographical references (leaves 114-124).

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by Lo Yuk-ming. / Bibliography: leaves 56-59 / Thesis (M.Ph.)--Chinese University of Hong Kong, 1985

The gelling characteristics of whey proteins is governed by factors which affect the structural properties of the protein. To understand this structure gelling relationship, the following factors were investigated; protein concentration, heating temperature and time, pH, NaCl and sugars. The effect of these factors on the molecular structure and gelatin properties of whey protein concentrate (WPC), $ beta$-lactoglobulin ($ beta$-lg), $ alpha$-lactalbumin ($ alpha$-lac) and bovine serum albumin (BSA) were studied using polyacrylamide gel electrophoresis, HPLC, mass spectrometry, differential scanning calorimetry and Fourier transform infrared spectroscopy. The results showed that protein concentration affected textural properties without affecting the molecular structure of the whey proteins while heating temperature, pH and NaCl affected both molecular structure and the textural characteristics. NaCl and sugars increased the stability of whey proteins to thermal denaturation but decreased gel formation. $ beta$-lg formed an opaque gel at pH 3 and a translucent gel at pH 9; the peak temperature of denaturation was 84$ sp circ$C at pH 3 and 70$ sp circ$C at pH 9. At both acid and alkaline pH, denaturation of $ beta$-lg resulted in the formation of intermolecular $ beta$-sheet structures associated with aggregation. These $ beta$-sheet aggregate structures were also observed when $ alpha$-lac was heated at pH 3 and 5 but not at pH 7 and 9. At pH 7, heating $ alpha$-lac resulted in a loss of $ alpha$-helix, $3 sb{10}$-helix and $ beta$-sheet and an increase in turns. DSC showed two reversible transitions at 39.6$ sp circ$C (A) and 64.8$ sp circ$C (B). At pH 3, transition A was partially reversible (14%) while transition B was completely reversible. At pH 9, transitions A and B were completely irreversible and a translucent gel was formed. Bovine serum albumin (BSA) showed maximum stability to thermal denaturation at pH 5. Denaturation of BSA resulted in the loss of $

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Whey Protein Concentrate (WPC) is used as a functional ingredient in many food products. To increase the applicability of WPC as well as other food proteins, it is often necessary to enhance the functional properties of the protein. Various protein modification techniques can be used for this purpose; this includes chemical, physical and enzymatic modification. In present study acid hydrolysis, a chemical modification, was investigated as a means to improve functionality of WPC, emulsifying, foaming and gelatin. Most of the previous work on WPC has been directed at enzymatic hydrolysis. / Dispersions of WPC (8%) in organic acids (0.5 N, 1 N and 1.5 N acetic acid, citric acid phosphoric acid and mixture of these acids) were subjected to acid hydrolysis (6, 18 and 48 h) and the effects of this modification on functional properties was assessed. The degrees of hydrolysis were measured and freeze-dried hydrolysates were evaluated for their foam capacity and stability, emulsifying activity and stability index and toughness. Highest foam capacity was found in the hydrolysate obtained using 0.5 N acetic acid (6 h hydrolysis, foaming capacity of 140%); acid hydrolysis increased foam stability, in general. In addition, acid hydrolysis did not affect emulsifying activity index but gave higher emulsifying stability index and toughness of prepared gels. / Results of PAGE indicated that acidic modification led to progressive decrease in the $ alpha$-lactalbumin and BSA. $ alpha$-lactalbumin was found to be the most sensitive protein with significant degradation after 6 h hydrolysis. (Abstract shortened by UMI.)

Thesis (Ph.D.). / Written for the Dept. of Food Science and Agricultural Chemistry. Title from title page of PDF (viewed 2009/06/05). Includes bibliographical references.

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